Staphylococcus aureus is a significant human pathogen which can produce a variety of toxins, including the exotoxin, staphylococcal enterotoxin B (SEB). SEB is highly toxic in small doses, and the compact structure of this protein makes it resistant to heat and denaturation. The combination of toxicity and stability caused this toxin to be selected for weaponization in the 1960s as a biowarfare agent for aerosol dispersal. In fact, it has been suggested that SEB is one of the "two most important toxin threats on the battlefield or in bioterrorism". Unfortunately, no effective vaccine exists that provides protection against this category B agent of bioterrorism. In previous Phase I studies, we demonstrated our ability to express a non-toxic form of SEB at high levels in transgenic soybeans. Oral immunizations using soy milk formulations made from transgenic seeds expressing mutant SEB could elicit protective immunity in mice challenged with lethal doses of native toxin. In the present Phase II studies, we will demonstrate the efficacy of immunization with our soybean-derived vaccine using a highly relevant piglet model of SEB toxicity. Since SEB is also a superantigen for pigs, the toxicity induced in these animals following exposure to the native toxin provides a valuable model for assessing the efficacy of vaccination. In collaboration with Drs. Stahl and Odle at N.C. State University, we will use this model to define dosing and safety of our soybean- derived vaccine using several immunization strategies. Immune piglets will then be challenged with native SEB to demonstrate the ability to protect animals from exposure to this toxin. Due to the relevance of the model, results from these studies will be translational to developing a human vaccine. Due to the novel nature of our platform technology for expressing immunogens in transgenic soybeans, there are no clear standards for GMP production of soy meal containing a vaccine. Therefore we propose initial studies to begin to establish the procedures which will be required to produce uniform lots of vaccine that will be safe for processing to final formulations. In the end, the completion of these Phase II studies will provide necessary information to fulfill some of the requirements set by the FDA for developing vaccines against agents of bioterrorism. PUBLIC HEALTH RELEVANCE: Staphylococcal enterotoxin B (SEB) is highly toxic in small doses, and the compact structure of this protein makes it resistant to heat and denaturation. The combination of toxicity and stability caused this toxin to be selected for weaponization in the 1960s as a biowarfare agent for aerosol dispersal. Unfortunately, no effective vaccine exists that provides protection against this category B agent of bioterrorism. In the present Phase II studies, we will demonstrate the efficacy of immunization with our soybean-derived vaccine using a highly relevant piglet model of SEB toxicity. The completion of these Phase II studies will provide necessary information to fulfill some of the requirements set by the FDA for developing vaccines against agents of bioterrorism.